1. Field of the Invention
This invention concerns a monolithic catalyst support of a monolithic catalyst for purifying exhaust gases from internal combustion engines and, more specifically, it relates to a monolithic catalyst support improved with the durability by enhancing the depositing strength of a carrier layer formed on the surface of a metal substrate for a monolithic catalyst support.
2. Description of the Prior Art
Monolithic catalysts have generally been used as catalysts for the purification of exhaust gases from internal combustion engines, particularly, automobiles engines. The monolithic catalyst usually comprises a monolithic catalyst support and catalyst ingredients carried on the support. The support usually comprises a monolithic substrate and a porous catalyst carrier layer of active alumina having large surface area formed on the surface of the monolithic substrate. It has recently been proposed to form the substrate with a heat-resistant metal comprising a composition of aluminum, iron, chromium (refer to Japanese Patent Laid-Open No. 68143/1982).
In a metal substrate, an oxide membrane such as an .alpha.-alumina membrane is usually formed on the surface layer of the substrate by applying heat treatment to the substrate. However, since the membranes do not have a good affinity for the active alumina carrier layer fixed on this membrane, the deposition strength between the active alumina layer and the metal substrate is not sufficient thus possibly leading to the defoliation of the active alumina layer during use.